We have hypothesized that platelet secretory products could be toxic to CNS neurons, and be significant in ischemic neuronal injury. This hypothesis has been supported by our recent work in which organotypic rat spinal explants were exposed to platelets and platelet secretory products. Since our initial report, additional studies have continued to show evidence of platelet-mediated neurotoxicity. Further, using the same technique, we identified serotonin (5HT), a major platelet product, to be a neurotoxin. This 5HT-neurotoxicity was demonstrable at concentrations that may be present in brain tissue surrounding an acute thrombus. The pronounced neurotoxic effect of 5HT was prevented by prior treatment of the explants with ketanserin, a specific 5HT2 antagonist. This suggests that the 5HT- neurotoxicity may be receptor-mediated. In the present application, we proposed to: a) study the existence of other neurotoxins in platelet secretion, and b) study the mechanism of 5HT-neurotoxicity. Both organotypic and immortalized cell line (PC12) cultures will be employed to document neurotoxicity, whereas, only the latter will be utilized to address the mechanism of 5HT neurotoxicity. Experiments will be conducted to test if 5HT is toxic via a physiological pathway involving signal transduction and transcription regulation. The studies proposed in the application could provide valuable insight into the significance of platelet secretory products to neuronal injury in general and thrombotic stroke in particular. The findings could potentially open new approaches to stroke treatment.